Dewatering fine coal slurries using two types of organopolysiloxanes

Abstract

Aqueous slurries of fine coal are dewatered by a process which comprises mixing a mixture of a water-soluble organopolysiloxane and a water-emulsifiable organopolysiloxane with the slurry, separating the slurry to recover the fine coal and further drying the fine coal, if desired. The use of a mixture of a water-soluble organopolysiloxane and a water-emulsifiable organopolysiloxane unexpectedly provides improved separating and/or improved drying of fine coal compared to a dewatering process that uses only one of the organopolysiloxanes.

That which is claimed is: 
     
       1. A process for dewatering an aqueous slurry of fine coal, said process comprising (I) mixing a dewatering-improving amount of a water-soluble organopolysiloxane plus a water-emulsifiable organopolysiloxane with the aqueous slurry of fine coal, said water-soluble organopolysiloxane and said water-emulsifiable organopolysiloxane having the formula R a  H b  SiO.sub.(4-a-b)/2 wherein a and b are numbers, the sum of which has an average value of from greater than zero to less than four, b has an average value of from zero to a and R denotes an organic radical bonded to a silicon atom by a silicon-carbon bond, the weight ratio of the water-soluble organopolysiloxane to the water-emulsifiable organopolysiloxane having a value of from 1/99 to 99/1,   (II) separating the organopolysiloxanes-containing aqueous slurry of fine coal into an aqueous portion and a fine coal portion, said fine coal portion having a water content of less than 20 percent by weight.   
     
     
       2. The process of claim 1 wherein said aqueous slurry of fine coal is the product of a flotation process. 
     
     
       3. The process of claim 1 wherein said aqueous slurry of fine coal has a water content of from 65 to 75 percent by weight. 
     
     
       4. The process of claim 1 wherein said separating comprises a filtering process. 
     
     
       5. The process of claim 1 wherein the fine coal portion containing less than 20 percent by weight water is dried by a heating process to further reduce the water content thereof. 
     
     
       6. The process of claim 1 wherein said fine coal has a nominal particle size of 28 to 200 mesh. 
     
     
       7. The process of claims 1, 2, 3, 4, 5 or 6 wherein the water-soluble organopolysiloxane is a methylorganopolysiloxane wherein at least 50 percent, but not all, of the R radicals therein are the methyl radical, the balance of R radicals being polyethyleneoxy-substituted radicals. 
     
     
       8. The process of claims 1, 2, 3, 4, 5, or 6 wherein the water-emulsifiable organopolysiloxane is a methylorganopolysiloxane wherein at least 50 percent, but not all, of the R radicals therein are the methyl radical, the balance of R radicals being polypropyleneoxy-substituted radicals. 
     
     
       9. The process of claims 1, 2, 3, 4, 5 or 6 wherein the water-soluble organopolysiloxane has the formula Me 3  SiO(MeYSiO) 10 ±5 SiMe 3  and the water-insoluble organopolysiloxane has the formula Me 3  SiO(Me 2  SiO) 67  (MeZSiO) 3  SiMe 3 , Me denotes methyl, Y denotes --CH 2  CH 2  CH 2  (OCH 2  CH 2 ) 12  OH and Z denotes --CH 2  CH 2  CH 2  (OCH 2  CH(CH 3 )) 2 .5 OH. 
     
     
       10. The process of claim 9 wherein the weight ratio of the water-soluble organopolysiloxane to the water-emulsifiable organopolysiloxane has a value of from 20/80 to 80/20.